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Laser project (prop)
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Jester:
I have no experience with lasers...

My sister is in the movie set construction business and asked me if I could make an ac powered laser prop that would shine an array of 5 visible red lasers. They want two arrays of 5 beams, and they need to project 5' minimum.

They were planning to use off the shelf laser pointers however holding the buttons and batteries are proving problematic.

If I orders these: https://www.ebay.com/itm/10Pcs-5V-650nm-5mW-Red-Dot-Laser-Module-Laser-Diodes-Sights-Laser-Pointers/192103230336?hash=item2cba3eab80:g:qsMAAOSwJ7RYUPzb:rk:2:pf:0
do I need a lens or should I expect these to work if I simply connect them with a 5Vdc wall wort?


abraxa:
They'll create a dot on whatever surface the beam hits but don't expect the beams themselves to be visible.
In order for the beams to be visible, you'll need either smoke/fog or powerful lasers that are EXTREMELY dangerous.

5mW is as high as I would go - some would argue that anything more than even 1mW is too much if you can't make sure that no one looks into the beams with their eyes. In my opinion, anything more than 5mW is asking for ruined lives, trouble and lawsuits.

Safety dictates a low power output, so you'll want to make sure that the beam is as visible as possible. The human eye perceives a wave length of 635nm as significantly brighter than 650nm, so I'd definitely use 635nm modules. Green at 532nm (540nm) is even more visible but red is less dangerous to use (no infrared emission of unknown power) and... well... they asked for red :)

Some visuals if you care for them:
[635 vs 650nm comparison]
[Green Lasers: What Can Certain mW Do?]
PointyOintment:

--- Quote from: abraxa on October 27, 2018, 08:55:24 am ---Safety dictates a low power output, so you'll want to make sure that the beam is as visible as possible. The human eye perceives a wave length of 635nm as significantly brighter than 650nm

--- End quote ---
But does the camera? This is for a movie prop.
Wolfram:

--- Quote from: PointyOintment on October 29, 2018, 07:28:50 am ---
--- Quote from: abraxa on October 27, 2018, 08:55:24 am ---Safety dictates a low power output, so you'll want to make sure that the beam is as visible as possible. The human eye perceives a wave length of 635nm as significantly brighter than 650nm

--- End quote ---
But does the camera? This is for a movie prop.

--- End quote ---

If the camera-display system has a reasonable white-balance, then by definition colors in the reproduced image will have similar relative brightness to reality.
dmills:
Be careful with laser display stuff around video cameras, the sensors really do not like being hit with the small spot size that results from a reasonable correlated laser source hitting the lens.... Film cameras are actually significantly better in this respect (You don't usually ruin the camera), but exposure can be tricky.

You will find that the lasers look significantly brighter if filmed from almost on axis as the dust in the atmosphere preferentially scatters the light at small angles, push comes to shove a 'hazer' (Something like a DF-50 diffusion machine) will make the beams FAR more visible (But talk to your lighting cameraman about that).

You really want to be posting this over on Photonlexicon where the laser geeks hang out.

Regards, Dan.
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